Innersoles, especially those containing arch supports, have been used historically to relieve foot and leg discomfort due to flat or low arches, high arches, over-pronation, over-supination, valgus, varus, and a variety of other conditions. The function of the longitudinal arch is to provide a flexible, shock absorption mechanism for the body while standing, walking, running, etc. When this mechanism is not functioning properly, several disorders can develop.
Pronation is the tendency for the longitundinal arch to depress and roll inward. This action is usually accompanied with a rolling inward and downward of the medial side of the foot and ankle, an outward rotation of the heel and an outswing of the forefoot. Some people with flat or low arches experience excessive pronation, also known as overpronation. Discomfort in the arch of the foot is common in persons with over pronation because excessive repetitive stress is placed on joints and ligaments in the midpart and hind-part of the foot. Leg fatigue and discomfort is also common because there is an overuse of leg muscles which resist the repetitive depression of the arch. In some instances, arch supports are prescribed after bunion surgery because overpronation can lead to a recurrence of bunion deformities. These devices typically help by realigning the foot to achieve a neutral positioning of the bone structures. Some of these devices employ subtle or passive methods of cushioning to achieve a comforting effect while others use rigid or force-fit methods of realigning the foot. Many innersoles require fitting to a shoe size that is larger than the user would typically wear. This indicates that most innersoles are too bulky to provide a comfortable, non-restrictive fit in properly sized shoes when both the foot and the arch support occupy the same space. Others are trimmed to fit the shoe. Other devices are constructed with laminated foams and then thermoformed or compression molded to achieve a contoured effect. Laminated articles have the potential for delaminating over time, with use. These devices typically blend a heel cup with the arch cushion to stabilize the rear foot in addition to supporting the longitudinal arch. Full length shoe inserts, which utilize polyurethane foam molding technology, are shaped similarly to the formed foam devices in that a contoured heel cup and blended arch cushion are predominant structures in the device. Most of these devices employ some type of topcover for visual and performance reasons. They also tend to crowd the foot due to the toe area having a full thickness of cushioning material as well as an over cushioning of the heel which tends to raise the ankle, thereby losing the support of the shoe itself.
By way of example, U.S Pat. No. 4,823,420 discloses a contour molded insole for footwear including an insole blank shaped to include an upwardly concave surface portion which, under pressure, is caused to invert to form a convex surface. U.S. Pat. No. 4,756,096 discloses a custom molded insole for supporting the foot in a ski boot made of a thin, formed blank of semi-rigid, bendable resilient material molded to the contour of the plantar surface/sole of a human foot, wherein the blank extends along the full length and width of the foot. U.S. Pat. No. 4,627,177 discloses a footwear insole member made of a first portion in which the area of the upper surface approximately underlies the area of the longitudinal arch and a second portion the area of the upper surface of which underlies at least about 10% of the medial area of the heel and from 0 to about 50% of the lateral area of the heel. U.S. Pat. No. 4,619,056 discloses an insole with integrally molded ridges to provided enhanced support for the foot in the region of the arch. U.S. Pat. Nos. 4,627,178 and 4,694,589 disclose an elastomeric shoe innersole made of a molded, elastomeric polyurethane foam material of low compression set, the heel and arch sections directly bonded in the molding process to a full-sole material composed either of foam or a solid, flexible sheet material. U.S. Pat. No. 4,674,204 discloses a shock absorbing innersole similar to that of U.S. Pat. No. 4,694,589, and also containing a solid, shock-absorbing heel insert. U.S. Pat. No. 4,586,273 discloses a shoe insert for reducing impact to the foot made of a base layer of a relatively resilient material, a foam layer disposed over the base layer and the means for integrally forming the base layer, foam layer and fabric into a sheet tri-laminate. U.S. Pat. No. 4,580,356 discloses a removable insole for shoes, the original profile of which is flat or curved, and which due to different grooves, gradually becomes permanently deformed on contact with the foot and finally adopts the profile thereof. U.S. Pat. No. 4,513,518 discloses an inner sole with a cushioning layer of polyurethane foam, with compression set less than 10%, laminated to a thinner layer of thermoformable polyethylene foam, which serves primarily as a vehicle for shaping the polyurethane. U.S. Pat. No. 4,338,734 discloses a universal orthotic which includes a monolithic shell, which may include a heel post, a navicular flange and a metatarsal raise, all formed monolithically to facilitate its manufacture. U.S. Pat. No. 2,034,563 discloses a longitudinal arch supporting shoe element composed of an inner sole split from its heel end into its ball portion, the split portion includes a relatively thick bottom layer and a thinner top layer. U.S. Pat. No. 2,965,984 discloses an arch supporting insole having a top sheet of plastic film, a thicker sheet of plastic foam beneath the top sheet, a partial bottom sheet of plastic film beneath the foam sheet, a heat seal seam joining all of the sheets and defining the bounding edge of the insole. U.S. Pat. No. 2,803,895 discloses a protective innersole made of a plurality of stacked laminates including a top laminate, a bottom laminate, each of said laminates having a pair of ends and an area substantially coextensive with the sole. U.S. Pat. No. 1,466,386 discloses a foot support adapted to be worn inside a boot or shoe, an insole, an uncovered semi-circular pad of sponge rubber cemented to the underface of the insole at the longitudinal arch, and an attaching strip secured to the pad and insole for holding the pad more firmly in position. Most of these innersoles are too bulky to fit within a normal shoe, causing the foot to be overly restricted within the shoe.
There is a need to provide a thin, removable, non-slip innersole that provides arch support through material resilience and yet has structural resilience to allow for a comfortable fit for both the feet and the innersole in a shoe. There is also a need to provide a three dimensionally contoured, wholly molded innersole which can provide cushioning and/or support and which takes up less space in the shoe than other known innersole and which will allow the foot to move normally within the shoe. It would also be desirable to provide an innersole which is durable, i.e. retains its original shape, resiliency, and remain as one piece. It would also be desirable to provide a lightweight, flexible innersole that can fit most footwear styles, with little or no trimming needed.